1CLOCK_NANOSLEEP(2)         Linux Programmer's Manual        CLOCK_NANOSLEEP(2)
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NAME

6       clock_nanosleep - high-resolution sleep with specifiable clock
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SYNOPSIS

9       #include <time.h>
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11       int clock_nanosleep(clockid_t clock_id, int flags,
12                           const struct timespec *request,
13                           struct timespec *remain);
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15       Link with -lrt.
16
17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       clock_nanosleep(): _XOPEN_SOURCE >= 600
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DESCRIPTION

22       Like  nanosleep(2), clock_nanosleep() allows the caller to sleep for an
23       interval specified with nanosecond precision.  It differs  in  allowing
24       the  caller  to select the clock against which the sleep interval is to
25       be measured, and in allowing the sleep  interval  to  be  specified  as
26       either an absolute or a relative value.
27
28       The time values passed to and returned by this call are specified using
29       timespec structures, defined as follows:
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31           struct timespec {
32               time_t tv_sec;        /* seconds */
33               long   tv_nsec;       /* nanoseconds [0 .. 999999999] */
34           };
35
36       The clock_id argument specifies  the  clock  against  which  the  sleep
37       interval  is to be measured.  This argument can have one of the follow‐
38       ing values:
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40       CLOCK_REALTIME   A settable system-wide real-time clock.
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42       CLOCK_MONOTONIC  A non-settable, monotonically  increasing  clock  that
43                        measures time since some unspecified point in the past
44                        that does not change after system startup.
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46       CLOCK_PROCESS_CPUTIME_ID
47                        A settable per-process clock that  measures  CPU  time
48                        consumed by all threads in the process.
49
50       See clock_getres(2) for further details on these clocks.
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52       If flags is 0, then the value specified in request is interpreted as an
53       interval relative to the  current  value  of  the  clock  specified  by
54       clock_id.
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56       If  flags  is TIMER_ABSTIME, then request is interpreted as an absolute
57       time as measured by the clock, clock_id.  If request is  less  than  or
58       equal to the current value of the clock, then clock_nanosleep() returns
59       immediately without suspending the calling thread.
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61       clock_nanosleep() suspends the execution of the  calling  thread  until
62       either  at least the time specified by request has elapsed, or a signal
63       is delivered that causes a signal handler to be called or  that  termi‐
64       nates the process.
65
66       If  the  call  is  interrupted  by  a signal handler, clock_nanosleep()
67       returns -1, and sets errno to EINTR.  In addition,  if  remain  is  not
68       NULL, and flags was not TIMER_ABSTIME, it returns the remaining unslept
69       time in remain.  This value can then be used to call  clock_nanosleep()
70       again and complete a (relative) sleep.
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RETURN VALUE

73       On  successfully sleeping for the requested interval, clock_nanosleep()
74       returns 0.  If the call is interrupted by a signal handler  or  encoun‐
75       ters an error, then it returns a positive error number.
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ERRORS

78       EFAULT request or remain specified an invalid address.
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80       EINTR  The sleep was interrupted by a signal handler.
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82       EINVAL The  value  in  the  tv_nsec  field  was  not  in the range 0 to
83              999999999 or tv_sec was negative.
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85       EINVAL clock_id was invalid.  (CLOCK_THREAD_CPUTIME_ID is not a permit‐
86              ted value for clock_id.)
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VERSIONS

89       The clock_nanosleep() system call first appeared in Linux 2.6.  Support
90       is available in glibc since version 2.1.
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CONFORMING TO

93       POSIX.1-2001.
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NOTES

96       If the interval specified in request is not an exact  multiple  of  the
97       granularity  underlying  clock (see time(7)), then the interval will be
98       rounded up to the next multiple.  Furthermore,  after  the  sleep  com‐
99       pletes,  there may still be a delay before the CPU becomes free to once
100       again execute the calling thread.
101
102       Using an absolute timer is useful for preventing timer  drift  problems
103       of  the type described in nanosleep(2).  (Such problems are exacerbated
104       in programs that try to restart a relative  sleep  that  is  repeatedly
105       interrupted by signals.)  To perform a relative sleep that avoids these
106       problems, call clock_gettime(2) for the desired clock, add the  desired
107       interval  to  the  returned time value, and then call clock_nanosleep()
108       with the TIMER_ABSTIME flag.
109
110       clock_nanosleep() is never restarted after being interrupted by a  sig‐
111       nal  handler,  regardless  of  the use of the sigaction(2) SA_SIGACTION
112       flag.
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114       The  remain  argument  is  unused,  and  unnecessary,  when  flags   is
115       TIMER_ABSTIME.   (An  absolute  sleep  can  be restarted using the same
116       request argument.)
117
118       POSIX.1 specifies that clock_nanosleep() has no effect on signals  dis‐
119       positions or the signal mask.
120
121       POSIX.1  specifies  that after changing the value of the CLOCK_REALTIME
122       clock via clock_settime(2), the new clock value shall be used to deter‐
123       mine   the   time   at   which   a   thread   blocked  on  an  absolute
124       clock_nanosleep() will wake up; if the new clock value falls  past  the
125       end  of the sleep interval, then the clock_nanosleep() call will return
126       immediately.
127
128       POSIX.1 specifies that changing the value of the  CLOCK_REALTIME  clock
129       via  clock_settime(2)  shall have no effect on a thread that is blocked
130       on a relative clock_nanosleep().
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SEE ALSO

133       nanosleep(2), timer_create(2),  clock_getres(2),  sleep(3),  usleep(3),
134       time(7)
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COLOPHON

137       This  page  is  part of release 3.22 of the Linux man-pages project.  A
138       description of the project, and information about reporting  bugs,  can
139       be found at http://www.kernel.org/doc/man-pages/.
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143Linux                             2008-07-09                CLOCK_NANOSLEEP(2)
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